This invention relates to a free fall detection device capable of detecting a fall accompanied by rotation.
Devices that can improve an impact resistance by knowing when an object finishes falling include a magnetic disk. A magnetic disk has a greater impact resistance in a landing zone where a head is parked when it does not perform reading or writing than in an area where the head can perform reading or writing. Thus, by detecting a fall of the disk and move the head to the landing zone before landing, the impact resistance of the magnetic disk against the fall head can be enhanced.
An example conventional technique to realize the above function using an accelerometer involves deciding a free fall when outputs of accelerometers in three axial directions not on the same plane (e.g., orthogonal x, y and z axes) are almost zero simultaneously (see JP-A-2000-241442 for example).
In the above conventional technique, when a device to be protected rotates as it falls, the accelerometers detect a centrifugal force. So, the outputs of the accelerometers on all axes do not become almost zero at the same time, failing to detect the fall.
A problem that this invention aims to solve is to provide a free fall detection device capable of detecting a fall accompanied by rotation.